Touch screens are display overlays which are typically either pressure-sensitive (resistive), electrically-sensitive (capacitive), acoustically-sensitive (surface acoustic wave (SAW)) and/or photo-sensitive (infra-red). The effect of such overlays is to allow a display to be used as an input device, with such displays often attached to computers and/or networks. Currently, the most popular touch screen systems are resistive and/or capacitive.
A typical resistive display consists of a transparent glass panel covered with a conductive and resistive metallic layer. These two layers are separated by an array of insulating spacers, and an electrical current runs through the two layers while the display is operational. When a user touches the glass panel, the two layers make contact at an underlying point. The resulting change in the electrical field at that point is detected and the coordinates of the point are calculated by a computer. Resistive touch screen displays are generally the most affordable, but offer only 75% clarity and the transparent layer can be easily damaged by sharp objects.
In a typical capacitive system, a layer that stores electrical charge is placed on the glass panel of a display. When a user touches the display, a charge is transferred to the user, and the overall charge on the capacitive layer decreases. This decrease is detected by circuits located in the display (e.g., in the four corners), allowing a computer to calculate the point of contact. One advantage of capacitive displays is that they generally allow for greater light transmission than resistive systems, resulting in a much clearer picture in the former than in the latter.
Thus, it is apparent that a good transparent conductive material is key in both resistive and capacitive touch screen displays. Currently, the most common such materials are transparent conducting oxides (TCOs), specifically Indium-tin-oxide (ITO) on glass. However, ITO can be an inadequate solution for many emerging applications (e.g., touch screens given that ITO is relatively brittle), and the Indium component of ITO is rapidly becoming a scarce commodity. Hence, a more robust and abundant transparent conductor is required.